1. Field of the Invention
This invention relates to a one-component moisture curable urethane sealant composition which can be used for such applications as a sealant, an adhesive, and a coating agent for automobile, construction, and structural purposes. More specifically, this invention relates to a one-component moisture curable urethane sealant composition which exhibits high curing speed, no adhesion failure upon catalytic acceleration of the curing, excellent storage stability in the absence of moisture, sufficient curability in the presence of atmospheric moisture, retention of adhesion even in the change of curing environment, and sufficient form retention after the coating of the sealant.
Furthermore, the present invention provides a moisture curable polyurethane composition which exhibits excellent adhesion to glass, resin, metal, and the like, and in particular, to aluminum as well as excellent curability, high foaming resistance, and good elongation even when no primer is used.
2. Background Art
Moisture-curable (one-component) polyurethane composition comprising the main component of urethane polymer and the curing agent (also referred to as the curing catalyst) has been widely used as an adhesive between metal surfaces, an adhesive between chassis and window glass, a sealant, and a coating agent in the fields of automobile production, construction, and structural engineering.
A moisture curable polyurethane composition generally contains a tertiary amine compound and/or a metal carboxylate as a curing catalyst, and the curing speed of the composition is adjusted by the type and the content of the curing catalyst.
Such moisture curable polyurethane composition has the merit that storage and working can be accomplished by handling the one-component composition. However, the curing speed and the storage stability are contradictory features and there is a problem that a composition enjoying a high curing speed essentially suffer from poor storage stability and vice versa.
Various curing agents have been investigated which fulfil the requirements for both the curing speed and the storage stability. For example, JP-B 5-75035 proposes use of dimorpholinodiethylether (DMDEE) as a catalyst for moisture curing of the urethane polymer which exhibits both sufficient storage stability and sufficient curability. JP-B 7-8982 proposes use of di[2-(3,5-dimethylmorpholino)ethyl]ether for improving low temperature curability of the DMDEE.
The dimorpholinodiethylether and its derivatives have no problems as long as they are used in normal environment. However, when used under high temperature, high humidity conditions, they are involved with the risk of debonding (PS) at the surface between the primer and the sealant. A reliable adhesion with the primer that is not affected by changes in the environmental conditions is highly awaited.
When the moisture curable polyurethane composition is used in automobile production line and the like for metal-to-metal adhesion or metal-to-glass adhesion, a primer such as silane coupling agent is usually applied to the adherend surface before the application of the polyurethane composition to thereby improve the curing speed and the adhesion.
Moisture curable polyurethane compositions which can be applied with no preliminary primer coating step are also investigated. For example, U.S. Pat. No. 4,374,237 proposes a polyurethane sealant containing a prepolymer having two or more silane groups per one molecule produced by reacting a urethane prepolymer with a secondary aminosilane. U.S. Pat. No. 4,687,533 proposes a polyurethane sealant containing a urethane prepolymer which has an alkoxysilane as its pendant group.
These polyurethane sealants, however, suffer from insufficient speed of curing, and for example, use of such sealant for adhesion of window glass to the chassis of an automobile is involved with safety problems. These polyurethane sealants also do not meet the requirements for the physical properties of structural materials.
U.S. Pat. No. 5,623,044 describes a polyurethane sealant containing the reaction product of a secondary aminosilane and a polyisocyanate. However, the polyurethane sealant containing such reaction product, namely, isophorone diisocyanate trimer, biuret modification of hexamethylenediisocyanates, polyphenyl polymethylene isocyanate, or the like suffers from the problem of insufficient initial adhesion. The large content of such modified isocyanate should adversely affect the physical properties of the sealant. Therefore, application of a primer containing a silane coupling agent is required when such polyurethane sealant is used for bonding a window glass to the chassis of an automobile.
JP-A 9-32239 proposes a method for dressing an exterior wall with tiles wherein a moisture curable urethane-based adhesive is described. In JP-A 9-32239, a urethane prepolymer is produced by reacting a trifunctional polyol and a polyisocyanate compound, and the urethane prepolymer is blended with an amino silane coupling agent and a glycidyl silane coupling agent to produce the moisture curable urethane-based adhesive.
A moisture curable polyurethane composition also suffers from the problem of foaming caused by the generation of carbon dioxide in the course of curing due to the reaction between the free isocyanate in the urethane prepolymer and the moisture. Such foaming is particularly significant under high temperature, high humidity conditions, and such foaming has been a serious problem in the use of the moisture curable polyurethane composition for applications such as sealing material and automobile sealant wherein the composition is exposed to high temperature, high humidity conditions in the course of the curing.
In view of the situation as described above, there is a strong demand for a polyurethane sealant which has obviated the problems as described above, and which exhibits excellent adhesion to glass, metal, plastic, and coated steel plates even without using any primer.
Accordingly, first object of the present invention is to provide a one-component moisture curable polyurethane composition employing a dimorpholinodiethylether or a derivative thereof for the catalyst which has obviated the problem of adhesion failure upon accelerated curing; which has high storage stability as well as sufficient curability by the moisture in the atmosphere; and whose adhesion is not adversely affected by unfavorable change in the curing environment.
The inventors of the present invention have found that such object can be attained by using a morpholine compound catalyst comprising dimorpholinodiethylether in combination with N,N-dimethylaminoethylmorpholine, and the polyurethane composition of the present invention is thereby provided.
The inventors of the present invention have also made an extensive investigation for the moisture curable urethane sealant composition which can be used for adhesion of glass, metal, plastic, coated steel plate, and other materials even without using any primer, and found that such object can be attained by incorporating in the polyurethane composition a silane adduct (which may be hereinafter sometimes referred simply as an adduct) of a polyisocyanate compound of particular structure and a secondary aminoalkocysilane of particular structure as described below. Such moisture curable urethane sealant composition is also provided.
The present invention also provides a novel polyurethane composition comprising the adduct as described above and (Bxe2x80x2) at least one tertiary amine catalyst having morpholino group and/or dimethyamino group, which may be the morpholine catalyst of the present invention as described above.
Accordingly, the present invention provides a moisture curable polyurethane composition comprising
(A) a urethane prepolymer, and
(B) a morpholine catalyst comprising
(i) a dimorpholinodiethylether represented by formula (1): 
xe2x80x83wherein n is 0, 1, or 2, and
(ii) a N,N-dimethylaminoethylmorpholine represented by formula (2): 
In the polyurethane composition, the content of the dimorpholinodiethylether (i) is preferably less than 0.15% by weight.
The preferable content of the N,N-dimethylaminoethylmorpholine (ii) in the polyurethane composition is generally in the range of 0.04 to 2% by weight.
The moisture curable polyurethane composition may further comprise 2 to 20% by weight of heavy calcium carbonate (C) having an average particle diameter of 1.0 to 3.2 xcexcm, and the thus composition is appropriate for a sealant.
The present invention also provides a moisture curable polyurethane composition comprising
(A) a urethane prepolymer,
(Bxe2x80x2) at least one tertiary amine catalyst having morpholino group and/or dimethyamino group, and
(D) at least one silane adduct selected from the group consisting of
(D-1) a silane adduct obtained by addition reaction between
a polyisocyanate which is a product of urethane reaction between at least one member selected from xylene diisocyanate, 1,3- or 1,4-di-(isocyanate methyl)cyclohexane, and derivatives thereof, and a compound having at least three active hydrogen atoms, and which has at least three isocyanate groups in one molecule, and
a secondary aminoalkoxysilane wherein the nitrogen atom has bonded thereto an aromatic ring or its derivative, and
(D-2) a silane adduct having a lysine skeleton obtained by addition reaction between a lysine isocyanate having 2 or 3 isocyanate groups and a secondary aminoalkoxysilane wherein the nitrogen atom has bonded thereto an aromatic ring.
The tertiary amine catalyst (Bxe2x80x2) may comprise a morpholine catalyst (B) comprising
(i) the dimorpholinodiethylether represented by the formula (1), and
(ii) the N,N-dimethylaminoethylmorpholine represented by the formula (2).
The composition may preferably contain, as the tertiary amine catalyst (Bxe2x80x2), 0.05 to 0.15 parts by weight of dimorpholinodiethylether (i) and 0.05 to 2 parts by weight of N,N-dimethylaminoethylmorpholine (ii) per 100 parts by weight of the total of the urethane prepolymer (A) and the silane adduct (D).
The tertiary amine catalyst (Bxe2x80x2) may be bis(2-dimethylaminoethyl)ether (iii) represented by the following formula (3): 
The polyurethane composition containing the tertiary amine catalyst (Bxe2x80x2) may further comprise (E) at least one member selected from the group consisting of a phosphite compound, a phosphonous acid ester compound, phosphinous acid ester compound, a phosphine compound, and mixtures thereof. Incorporation of the organophosphorus compound (E) is particularly desirable when the compound (Bxe2x80x2) is bis(2-dimethylaminoethyl)ether (iii).
Preferably, the moisture curable polyurethane composition of the present invention further comprises (F) an organotin compound.
The composition may preferably contain 0.002 to 0.1 parts by weight of said organotin compound (F) per 100 parts by weight of the total of the urethane prepolymer (A) and the silane adduct (D).
The urethane prepolymer (A) used in the present invention is generally a urethane prepolymer having free isocyanate group.